Thermal relay



Dec. l8 1934.

W. J. HUDSON THERMAL RELAY Filed Feb. 19, 1932 3 6 Q ff 4 66 67 4Sheets-Sheet l INVENTOR Will/zw J//udso/v.

Dec. 18,1934.v w. J. HUDSON THERMAL RELAY Filed Feb. 19, 1932 4Sheets-Sheet 2 W. J. HUDSON Dec. I8, 1934.

THERMAL RELAY 4 Sheets-Sheet 3 Filed Feb. 19, 1932 INVENTOR W/fsm HudsonWIVTNESSES ATTORNEY Dec. 1s, 1934. W, J, HUSON 1,985,033

THERMAL RELAY /6 3 -fmIm-Uwfije 5.

-|INvENToR Wil/dam Hudson ATTORNEY Panarea Dee. 1s, 1934 UNITED sTATEsPATENT oFElcE THERMAL RELAY Application FebruarylS, 1932, Serial No.593,994 43 Claims. (Cl. F75-336) My invention relates to relays andparticularly to thermal relays.

An object oi my invention is to provide a relatively simple thermalrelay having time delay and instantaneous operating characteristics.

Another object o! my invention is to provide.`

a thermal relay that shall have a substantially instantaneous resetcharacteristic.

Other objects oi my invention will appear 25 from a description of thedevice and of its operating characteristics, as set forth in thespecication and the claims or as will be specically pointed out herein.

In practicing myv invention, I provide an en- 3u ergizing coil, whichmay be of the series coil -typeand which may embody a plurality ofsections each including a plurality of spaced turns, one end of eachsection extending longitudinally of the coil to support a magneticallyreversible 3;, member therebetween which establishes an elec-f tricalconnection between the coil sections. The magnetically reversible memberis normally engaged by'a movable armature which constitutes a part of amagnetic frame structure, one part y 4o of the frame .structure beingprovided .with a main gap traversed by substantially all o! the magneticiiux generated by the energizing coil and including also twoparallel-related portions, one of which is constituted in part by themag 45 netically vreversible member. The armature is biased normallyinto engagement o r into sub stantial engagement with the magneticallyreversible member and is magnetically restrained from moving awaytherefrom at moderate over- 50 loads until its magnetic characteristichas changed because of an increase of temperature therein. At excessiveover1oads, however, the disengaging force exerted by another magnet poleon the armature increases relatively to the 55 restraining force of themagnetically reversible member to a degree which is suillcient tooverpower the restraining force without any thermal change inthemagnetic characteristics of the magnetically reversible member.

In another form of my invention, I provide a 5 relatively simpleplural-turn energizing coil which is stamped out of a iiat piece o!metal to provide terminal portions at each end, lugs adiacent to theterminal portions to support the magnetically reversible member and anintermediate portion which may be provided with a differing number ofalternately oppositely-extending lateral slots therein to provide anintermediate portion ci relatively highohmic resistance to constitute ashunt circuit for l5 the magnetically reversible member supported on thelugs.

In the drawings,

4Figure 1 is a top plan view of a device embodying my invention.

Fig. 2 is a view in horizontal section therethrough taken on the lineII-II of Fig. 4,

Fig. 3 is a view in horizontal section therethrough takenvon the lineIII-III of Fig. 4,

Fig. 4 is a view in front elevation of a device embodying my invention,

Figs. 5 and 6 are views in top plan and in iront elevation,respectively, of a magnetically reversible member and heater,

Fig. '7 is a view partially in side elevation and partially in verticalsection on a broken plane indicated approximately at VII- VII in Fig. 4,

Fig. 8 is a view in side elevationof a thermal relay embodying myinvention and provided with a modied form of energizing coil, 35

Fig. 9 is a bottom plan view of an energizing coil, such as is shown inFig. 8, the terminal studs being shown as secured thereto, i

Fig. 10 is a front elevational view of the coil shown in Fig. 9,

Fig. 11 is a top plan view of a punched coil before shaping,

Fig. i2 is a perspective view of the coil shown in Figs. 9 to li,inclusive, provided with terminal studs and an associated magneticallyreversible member.

Fig. 13 is a schematic view in side elevation of the main elements ofone form of device embodying 'my invention.

Fig. 14 is a schematic View in side elevation of a further modiilcationof my invention.

Fig. 15 is a view in iront elevation of the device shown in Fig. 13.

Fig. 16 is a schematic view in side elevation of another modification ofthe device embodying my invention. f

Fig. 17 is a view in side elevation of another modification of deviceembodying my invention.

Fig. 18 is a view in front elevation of the device shown in Fig. 16. r p

Fig. 19 is a view in side elevation of another modification of deviceembodying my invention.

Fig. 20 is a view in front elevation of the device shown in Fig. 19.

Fig. 21 is still another view in side elevation of another modificationof the device embodying my invention.

Fig. 22 is a view in front elevation of the device shown in Fig. 21, and

Fig. 23 is a diagrammatic representation of an electric circuit to moreclearly illustrate, by analogy, the magnetic circuits of the deviceshown in Figs. 12 to 22, inclusive.

The thermal relay embodying my invention may be mounted on a suitablebase 31 of electric-insulating material, of substantially rectangularshape in loutline and having an uneven front surface to assist insupporting the other elements of the relay in proper relative operativepositions thereon, the outline of the front surface being shown morespecifically in Fig. 7 of the drawings. The base 31 may be securedagainst a supporting plate 32 which, as shown in Fig. 7 of the drawings,may be of metal although this is not an important detail as the base maybe mounted on a switchboard panel.

A magnetizable core member 33, which is shown in the drawings as beingof solid magnetic material, is supported against the front surface ofbase 31 by a holding or clamping bolt 34 extending through an opening inthe base.

An energizing coil for the core 33 and other magnetizable portions tobehereinafter specifically described includes two'coils 37 and 38 eachincluding a plurality of turns of copper or other suitable metal stripbent on edge, the individual turns of each coil section being spacedapart to assist, not only in cooling the conductor itself, in the usualmanner, but also to assist in cooling another member to be hereinafterdescribed. The two adjacent end portions of the coils 37 and 38 arelocated in the same transverse plane and are shown at 39 and 41 -in Fig.4, while the other end of each of the coil sections is so bent as toextend longitudinally of, and `parallel to, the axis of the coil and ofthe core 33. Thus, the end 42 of the outer coil 37 extends toward thebase 31 while the end 43 of the inner coil 38 extends away from the base31, the two end portions 42 and 43, however, extending parallel to eachother.

A bar of magnetically reversible material, such as invar, which may beof the general kind shown in Figs. 5 and 6 and there indicated by 44, iselectrically connected to the ends 42 and 43 of the coil sections and issupported directly thereby. While I may use the bar 44 by itself,causing it to be heated by the action of an electric current traversingit, I may also, as shown in Figs. 5 and 6 of the drawings, provide anauxiliary heater strip 46 which may be of any suitable metal, only theend portions of which are electrically connected to the end portions ofthe bar 44 as by welding or brazving metal 47, indicated in Fig. 6. Thebars 44 and 46 may be provided with holes 48 therein through which mayextend clamping bolts 49 in order to ensure that the electricalconnection between the magnetically reversible bar and the ends of thecoil sections shall be as good as may be possible to obtain. In order toassist in reducing the ohmic resistance I may braze or solder the bars44 and 46 to the ends 42 and 43 of the coils.

The other end portions 39 and 41 of the coil sections are suitablysecured to terminal'bolts or.

'and in order to provide proper insulation, I may use dished washers 52of electric insulating material and I may also make the base 31 ofgreater thickness as is shown more particularly in Fig. 7 of thedrawings.

The heater strip 46 may have a plurality of alternatelyoppositely-extending lateral slots therein as shown in Fig. 5 of thedrawings and while the spacing and width of the slots may be the samethroughout, I may vary both the spacing and the width of the slots as isshown in Fig. 5 of the drawings in order that the member 44, andparticularly the intermediate portion thereof, may be heatednon-uniformly. In order to assist this unequal heating of the bar 44 ofmagnetically reversible material, I may make it of different areas ofcross section, as is shown in Fig. 5 of the drawings.' If the lateralwidth of the intermediate portion of thc f bar 44 is made constant, itis obvious that the temperature rise of the bar 44, when used alone,will be a maximum at the midpoint thereof and that the temperature willdecrease towards the ends of the bar 44.

A magnetizable frame structure cooperating with the core 33 includes afront frame 53 which may be of substantially4 bar shape and may have itslower end secured against the core 33 by a bolt 54. At the upper end ofthe front frame 53,- I locate anv armature bracket 56, of substantiallyL-shape, which may consist of a punched plate of magnetizable materialwhich has a laterally extending slot 57 therein (see Fig. 4) so that thearmature bracket 56 may be moved laterally relatively to the front frame53 and be held in any predetermined position thereon by a plurality ofclamping screws 58.

The armature bracket 56, just mentioned, carries a movable armature 59which is of substantially straight but slightly laterally-deformedshape, as is shown more particularly in Fig. 7

of the drawings, and which is pivotally mounted on the armature bracket56. The pivotal action is obtained by bending the outer end into an arcwhich rolls on a flat non-magnetic spacer 60 which is used to avoid theinterfering action o f residual magnetism and also for other purposeshereinafter described. A pin 61 is fitted rigidly into the bracket 56and a second pinv 62 is also fitted rigidly into the rear inner end ofthe bracket 56. A compression spring 63 surrounds the pin 62 and ts intoa recess 64 in the upper surface of ,armature 59, a washer 66v and acotter pin 67 cooperating with the pin 62 to yieldingly hold thearmature 59 in a predetermined position.

A rear frame 68 of magnetizable material and of substantially L-shape isclamped against the front surface of base 31 by the bolt 34 and thc core33, and its upper, forwardly extending end 69 is secured against thebase 3l by a machine screw 70, as shown in Fig. 3 of the drawings.

At a point immediately back of' the movable armature 59, the rear frame68 carries a pair of aprons 71 and 72, for which see particularly Figs.3, 4 and 7 of the drawings. The aprons 71 and 72 are of substantiallyplate form and have extensions 71a and 72a bent forwardly so as to lieparallel to, and spaced from, the respective end portions 42 and 43 ofthe coils 37 and 38. The body portions of the aprons 71 and 72 aresecured to the insulating base 31 by' screws 73, and the forwardlyextending tabs 71a and 72a are secured to the coil terminals 42 and 43by the bolts 49. The two aprons 7l and 72 thus serve to support the twoends of the invar strip 44, which is secured to the coil-terminals 42and 23.

One of the aprons, such as 72, is of magnetic material, so as to carryflux from the rear end of the magnet-core 33, through the rear plate 68,to one end of the invar strip. The other apron 71 is non-magnetic.

Flux is taken off of the invar strip by means of the movable armature59, and thence to the front plate 53 and the front end of the magnetcore33.

of a circuit breaker.

The inner or rear end of the movable armature 59, which is magneticallyrelated to the invar strip, is provided with means for varying the airgap between the armature and the invar strip 44, and this means mayinclude a nonmagnetic adjusting nut 76 on an iron, or magnetizable,screw-threaded stud 77 which is welded, or otherwise rigidly secured, tothe movable armature 59. The adjustingnut 76 has a serrated peripheralange which is engaged by a locking pin 78 to hold it in anypredetermined position. This particular adjusting element of the thermalrelay constitutes no part of my present invention but is disclosed in acopending application, Serial No. 574,317, filed by W. M. Ellingson onNovember 1l, 1931, and assigned to the Westinghouse Electric andManufacturing Company.

The iron stud 77 at the rear end of the movable armature 59 is normallynearly in engagement with the invar strip 44,-where it is held bymagnetic attraction, aided slightly by the spring 63. When the invarstrip 44 is heated, by excessive current-flow, to a critical temperaturewhich may be of the order of 200 C., it loses its magnetic propertiesenough for the rear end of the movable armature to be lifted by themagnetic pull of the horizontal flange 69 of the rear plate 68.

The rear end of the armature is provided with a striker plate 79 whichwill thus be caused to strike the bottom end of an actuating rod 80,which rod is of substantially rectangular shape in lateral section andmoves in a forwardly projecting portion 81 of base 31.

The upper end of the actuating rod engages a switch arm 82 which ispivot-ed at 82a on a terminal stud 83 and is biased by a compressionspring 84 to have its free end normally in engagement with a contactterminal 85 which has a terminal stud 86 extending back through the base31 and its support. This switch may be connected in series circuitrelation with a source of electric energy and with a device to becontrolled, such as the actuating coil of a relay or The controlledmeans or circuit has not been shown, as devices of this general kind areold in the art and the device embodying my invention may cooperate withany one of a numberof different devices or controlled means of thisgeneral kind.

Means are provided in the relay, either to make the switch arm 82automatically return to its initial closed position wherein its free endengages the contact terminal 85, or to make it remain in its openposition so that it will be necessary for an operator to manipulate apart of the relay to causel resetting or reclosing of the switch 82. Thelast-mentioned means is shown on the drawings, and it includes a resetknob 87 movable manually in a direction laterally of the base 31 andengaging a leaf-spring 88 (see Fig. 2), one end of which is secured inthe inside of the casing-portion 81 by a machine screw 89. A small rigidor unyielding strip of metal 91 is provided to limit the rearwardmovement of the leaf-spring 88 when it is actuated by the reset knob87.The inner end of the reset knob 87 is provided with a laterallyprojecting lug 92 and by turning the reset knob 87, the lug 92 may becaused to iit into a recess in front of the leaf-spring 88, or it mayengage a shoulder portion 93v (see Fig. 2) to hold the reset knob in itsactuated position where the inner end thereof occupies the positionshown in broken lines in Fig. 2 of the drawings.

The actuating rod 80 is provided with a shoulder 94 (Fig. 7) which maybe engaged by the upper edge of the leaf-spring 88 if the spring is notheld out of its path of movement by the reset knob S7. Thus, if theinner end of the reset knob 87 occupies the position shown by the brokenlines in Fig. 2 of the drawings, the spring 88 will be bent inwardly tothe position shown by the broken lines of Fig. 2 and the actuating rod80 may move freely up and down in accordance with the movements of thearmature 59. If, however, the reset knob occupies the position shown bythe full lines in Fig. 2, the switch arm 82 will remain in itsdisengaged position when it has been moved thereto by the upwardmovement of actuating rod 80.

Referring to Figs.' 2 and 'l of the drawings, I have there illustratedthe use oi a sheet 96 of electric insulating material between the rearsurface of the base 81 and the supporting member 32 so that thepossibility of electrical breakdown from the head of the bolt 34 shallbe reduced as much as possible.

In Figs. 8 to 12, inclusive, I have illustrated a simple and easilymanufactured plural-turn energizing coil which I have found particularlyadvantageous in the construction of my improved relay. Referring irst toFig. 11 of the drawings, Ihave there illustrated the general shape of apunched plate 101 which I utilize in making a plural-turn energizingcoil. The energizing coil 101 of Fig. 11 includes terminal portions 102and 103, lug portions-104 and 105 immediately adjacent to the terminalportions 102 and 103, an intermediate portion 106 and arcuate connectingportions 107 and 108.

Fig. 12 of the drawings shows'a View, in perspective, of the completedcoil and it may be noted that, in the completely shaped or nished coilstructure, the lug 104 is bent substantially at right angles to theterminal portion 102 which terminal portion has connected thereto aterminal stud 109, it being noted that the method of connection of theterminal stud 109 to the terminal portion 102 of the coil is immaterialand is here shown as includinglr a brazed joint. The other lug, 105, isalso bent substantially at right angles to the terminal portion 103 andin the reverse direction to that in which lug 104 is bent. The outersurfaces of the lugs 104 and 105 are parallel to each other and acurrenttraversed magnetically-reversible bar 111 may be secured againstthe outer surface of the lugs, either by brazing alone, or by brazingand bolts extending therethrough in a manner well known in the art.

It may here be noted that the magnetically reversible members 44 and 111may be made up of any one of a number of different materials but Iprefer to use a nickel-steel alloy known as invar, having on the orderof 35% nickel, which has the property of being magnetizable at ordinaryroom temperatures but of losing its magnetic characteristics upon anincrease of the temperature to a predetermined value. Nickelsteelcontaining approximately 35 to 36% of nickel loses its magneticcharacteristics when heated to approximately 210 C. while a nickelsteelalloy containing a slightly larger percentage of nickel loses itsmagnetic characteristics at somewhat higher temperatures. I prefer touse a material which has a thermally variable magnetic characteristicsuch that it loses its magnetizable character at a temperature on theorder of 210 C. or even slightly above this value.

As shown in Fig. 12 of the drawings, the invar member 111 includesrelatively large end portions and one intermediate portion 112 which isof varying area in lateral section, as well as a second intermediateportion 113 which is of uniform area in lateral section, but other sizesand shapes of bars designed to provide the same characteristics forother ratings may be used.

Referring more particularly to Figs. 11 and 12, and to the intermediateportion 106 of the blank 101, as shown in Fig. 11, ll call attention tothe alternately oppositely-extending lateral slots 114 and 116 which sodivide the intermediate portion 106 as to provide a circuitous path forthe current traversing the coil, which path is of relatively high ohmicresistance, as compared to the ohmic resistance of the terminal portions102 and 103. I may use any desired even number of alternately oppositelyextending, lateral slots in the intermediate portion 106, to obtaindifferent resistances of the intermediate portion of the coil structure,whereby it is possible to correspondingly vary the value of the current,or rather the portion of the current, traversing the magneticallyreversible member 111.

It will be noted by reference to Fig. 12 of the drawings that the coilstructure there shown provides a two-turn coil which is relatively openand well ventilated so that it can carry a relatively large .currentwithout undue heating. The open construction is also advantageous inassisting in cooling the ends of the invar strip 111.

A thermal relay embodying the energizing 'coil illustrated in Figs. 9 to12 inclusive, is shown in side elevation in Fig. 8 of the drawings andas all of the other parts of the relay are the same as shown in Figs. 1to 7, inclusive, these other elements have been given the same numeralsas the parts in Figs. 1 to 7, inclusive.

While I have illustrated and described a specific embodiment of a framestructure including a movable armature, I do not desire to be limited toany particular form thereof, and in order to show some of the variousforms which my apparatus may take, I illustrate a number of such formsin Figs. 13 to 22, inclusive, which will now be described.

Referring to Fig. 13, I have illustrated a base 117, a magnet-core 118and an energizing coil 119 which is here shown as including only onesection, but which may take either the form shown in Fig. 7 of thedrawings or that shown in Fig. 8 of the drawings. The coil is providedwith terminal members either as set forth hereinbefore or in a mannerusual in the art.

A movable armature 121 may be of magnetizable material and ofsubstantially L-shape and it may be pivotally supported on anon-magnetic frame 122 upon which the armature is yieldingly held in apredetermined position by a spring 123 in a manner Well known in theart. A rear frame structure 124 is provided, the upper portion of whichis provided with two spaced pole pieces or pole faces 126 and 127, in amanner substantially the same or similar to that hereinbefore set forthin connection with Figs. 1 to '7, inclusive. A magnetically reversiblebar 128 is suitably supported and may be heated either by the currenttraversing it or by an auxiliary heater 129, the magnetically reversiblebar or the heater, as the case may be, being connected in series circuitwith the coil 119 to be traversed by the load current. The magneticallyreversible member 128 coresponds to the bar 44 of Fig. 7 or to the bar111 of Fig. 8, and the heater 129 of Fig. 13 corresponds to the bar 46of Fig. 5.

An adjusting screw 131 is mounted on the inner end of movable armature121. The armature actuates a push rod 132 which corresponds to theactuating rod and may be used to actuate a switch. It is to beparticularly noted that the lower end of the screw 131 is made ofconical shape in order that it may have smallarea engagement with themagnetically reversible bar 128. It may be noted further, that the outeror lower end of the armature 121 is normaily spaced away from the outerend of the magnetizable core 118.

Referring now to Fig. 14, the mechanical construction there shown is thecounterpart of that shown in Figs. 1 to 7, inclusive and 1 have,therefore, numbered the different elements thereof, insofar as possible,the same as in Figs. 1 to 7, inclusive. While I have shown a single coil119, it is to be noted that in actual practice either a plural-sectioncoil, as shown in Fig. 7, or a modified coil, as shown in Figs. 8 to 12,inclusive, may be used.

Referring to Fig. 16 of the drawings,I have there shown a relayembodying a coil 119, a core 118, a movable armature 121 supported by anon-magnetic frame 122 and a rear frame 133 which has a lower portion134 of L-shape extending forwardly from the base 117 and an upperforwardly-extending portion 135. A magnetically reversible bar 128 isprovided and a heater 129, as was hereinbefore set forth in connectionwith Fig. 13. A push rod 132 moves in a guide 136.

Referring to Fig. 17, I have there illustrated a modification of thedevice shown in Fig. 16 except that the front frame 122a is of magneticmaterial and a non-magnetic spacer 137 is provided between the frontframe 122a and the armature core 118.

In Fig. 19 of th'e drawings, I have illustrated a still furthermodification of a device embodying my invention including a coil 119surrounding a core 118, and a movable armature 138 which is pivotallymounted against a non-magnetic insert 139 and yieldingly held in itsinitial or normal position by a compression spring 140 on a pin 141. Therear magnetizable frame includes a lower portion 142 extending forwardlyfrom the base, a back portion 143 extending parallel to the base and a.magnetically reversible bar 144 which may be supported by the upper endof the back portion 143. An adjusting screw 146 is provided at the upperend of armature 138 and has a conical inner end to engage one edge ofbar 144.

Referring to Fig. 21 of the drawings, I have there shown a still furthermodification of a thermal relay embodying a core 118, a coil 119 and arear magnetizable frame having a lower frame-portion 147 extendingforwardly` at the base and a portion 148 extending parallel to the base.A magnetically reversible bar 149 is provided, as well as a heater 129.A front frame 151 of magnetizable material may be utilized to supportthe magnetically reversible member 149, being itself supported from thecore 118. A non-magnetic spacer 139 is located between the core 118 andthe front frame 151. A movable armature 152 has one end pivotallymounted on and engaging one end of the front frame 151, being yieldinglyheld in its normal position by a spring 153. The armature 152 is held insuch position that it is spaced from the outer end of the lower portion147 of the rear frame and is so disposed as to actuate a push-rod 132.

I will now set forth in greater detail the fundamental principles of themagnetic action and the magnetic characteristics of the frame structureand the movable armature which are made use of, in the operation of myimproved relay, to obtain a highly sensitive operation under varyingcurrent conditions. I have shown, in Fig. 23, an electric circuitanalogy by which it is expected to make clear the principles upon whichmy'improved relay is based.

Thus, it may be noted, by reference to Fig. 13, that there is an air gap154 in the magnetic circuit between the armature 121 and the front endof the magnetizable core 118, and this air gap is designed to have arelatively high magnetic reluctance and to be traversed bysubstantiallyall of the flux generated by the energizing coil 119. It is to beunderstood that, by substantially all of the flux, I mean that there isprovided no parallel path in this part of the magnetic circuit and that,therefore, only those flux-lines usually called leakage flux lines, willnot traverse this gap and the armature 121. Tracing the path of the fluxlines as they leave the core 118, it will be found that they willtraverse the armature 121 to the upper inner end thereof, where twoparallel magnetic circuits are provided, constituted as follows:

First, the portion 126 (Fig. 13), which is constituted by the forwardlyextending upward end portion 69 of the rear frame 68 as is shown in Fig.7 of the drawings. Second, the members 127 and 128 (Fig. 13), which, inthe device illustrated in Figs. l to 7 inclusive, are constituted by theforwardly extending portion 72a of the magnetizable apron 72 and the bar44 which has -a thermally variable magnetic characteristic as has beenhereinbefore set forth. The flux will therefore divide', a part thereofflowing from the armature 121 to the frame-portion 126 and the otherpart thereof (aside from the leakage ux) flowing through themagnetizable screw'131 into the invar bar 128 and thence to theframe-portion 127. The total flux will then flow through the rear frame124 and back to the core 118.

This general statement of the flux paths and the two parallel-relatedmagnetic reluctance portions connected in series circuit with the mainreluctance portion will hold for all the devices shown in the drawings,except that the high-reluctance main gap corresponding to the gap 154 inFig. 13 is provided by the non-magnetic insert 60 in Figs. 7 and 8, andby the nonmagnetic insert 137 in Figs. 14 and 17 and by the non-magneticinsert 139 in Figs. 19 and 21. Furthermore, the flux paths correspondingto the air-gap between the parts 121 and 126 in Fig. 13 is replaced bythe lower gap between the parts 121 and 134 in Figs. 16 and 17, betweenthe parts 138 and 142 in Fig. 19 and between the parts 152 and 147 inFig. 21.

Thus in Figs. 16 and 17, the flux will divide in armature 121, a partthereof flowing downward and passing from the lower end of the armature121 to the frame portion 134 and the other portion flowing upward to theinwardly extending horizontal end of armature 121 and thence through themagnetizable screw 131, and back to the core by a path similar to thatdescribed for Fig. 13. The flux from the air gap 121-134 will, ofcourse, return to the core 118 through the lower frame portion 134. InFigs. 19 and the flux divides in armature 138 at the end of core 118into a downwardly flowing portion which passes from the lower end of 138across an air gap into frame portion 142 and an upwardly flowing portionwhich passes from the upper end of 138 through an adjustablemagnetizable screw 146 and a thermally variable magnetic member 144 intothe upper portion of frame 143. In Figs. 21 and 22 the construction isthe same as Figs. 19 and 20 except that the upper portion of armature138 is made rigid as part 151 and the lower portion of armature 138alone is mobile and is shown as part 152.

Referring to Fig. 23, I have indicated, by the source of electric energy161, the magnetomotive source, (the energizing coil of the relay), whichsource of electric energy 161 sends a cur- -rent through a main resistor162, analogous to the main gap 60 in the thermal relay. From here thecurrent divides, a part thereof flowing through a resistor 163 whichcorresponds tothe magnetic reluctance between armature 121 and the xedmember 126 of Fig. 13, which gap may be designated as the pull-n gap. Aparallelrelated reluctance path in the frame structure of the relay isrepresented in Fig. 23 as including a resistor 164 corresponding to thereluctance of the small but unavoidable air gaps in the frame structure,a second resistance 166 corresponding to the relatively high magneticreluctance of the magnetically reversible bar 128 when hot, and a thirdresistance 167 corresponding to the relatively low magnetic reluctanceof the adjusting screw 131. A shunt circuit is shown across the resistor166, said shunt circuit being normally bridged by a short-circuiting bar168 which corresponds to the relatively very low magnetic reluctance ofthe invar member 128 or its counter part, which member has a lowmagnetic reluctance at low temperatures and is magnetizable, but whichloses its magnetic characteristic upon being heated to a predeterminedtemperature under certain operating conditions of the thermal relay.

Thus, when the energizing coll is traversed by a current of normalvalue, a relatively large amount of flux will flow from the armature 121through the gap to portions 127 and 128 of Fig. 13, which gap may betermed the hold-out gap.

It is therefore, evident that by far the greatest drop in magneticpotential will exist across main gap 154 (Fig. 13) whose counterpart isthe resistance 162 of Fig. 23. As the pull-in portion of the magneticcircuit, that is, the gap between armature 121 and member 126 of Fig. 13is bridged or shunted by the relatively low reluctance circuit includingmore particularly the magnetically reversible member 128, the magneticpull across the pull-in circuit acting on the armature 121 is,therefore, much lower than it would be if the structure providing maingap 154 were not present. The magnetic reluctance of the hold-out gap issmaller than the magnetic vreluctance of the main gap but the magneticreluctance of the pull-in gap is much larger than the magneticreluctance of the main gap.

It will thus be seen that all of the various modifications shown inFigs. 13 to 22 are characterized by the feature that an electricallyproduced magnetomotive force passes a flux across a main non-magneticgap, which may be an air gap and directly useful in producing magneticpull to move the armature as in Figs. 13 and 16, or it may be anon-magnetic spacer which is only indirectly useful in producing forceto move the armature by its influence on the magnetic distribution ofother parts of the system as in Figs. 14, 17, 19 and 21. A secondcharacteristic feature of all modifications is the provision of adivided return of the magnetic flux after it passes the non-magneticmain gap into two portions which are magnetically in parallel with eachother but in series with the main gap; any change in the reluctance ofone of the two parallel paths will produce a change in the flux passingthrough the other parallel path by change of the m. m. f. drop in themain gap, which is in series with both. It is characteristic of allmodifications that one return path (known as the pull-in gap) is an airgap between an armature portion and a magnetic frame portion and the uxacross this gap is solely or partly instrumental in producing motion ofthe armature when impediments to such motion in other parts of the relayare removed. It is characteristie of all modifications that the otherreturn path (known as the lockout path) is mainly in iron and in amagnetically reversible member and the amount of its flux is controlledby the special ferro-magnetic properties of those substances to preventor allow motion of the armature according to the size of the current andthe time it' flows. In all modifications except Figs. 21 and 22 theimpediment to motion exerted by the flux in the lockout path combines amechanical force directly exerted on the armature with the controllingeffect of the series-parallel arrangement ofmagnet gaps. In Figs. 21 and22 the lockout path does not produce any mechanical force directly butgoverns motion of the armature entirely by shunting more or less of theVmain flux away from the pull-in gap 152-132. The flux across the pull-ingap is never zero but for lower values of flux the armature is biased toits inoperative position by a spring 153.

Referring to Fig. 17, all of the flux passes into bracket 122-a andupward to the hinge point. At the hinge point the total flux divides andone portion flows downward to the lower end of 121 where it passesacross the pull-in air gap to frame portion 134. There is no magneticpotential to produce pull between 122-a and 121 but there is a largemagnetic potential difference between 121 and 134.

If now the magnetic conditions in the parallel related magnetic circuitportions are changed, as will occur upon heating of the magneticallyreversiblebar, the normally existing short circuit of the pull-in gap isremoved, analogous to opening of -contact bar 168 in Fig. 23, and themagnetic pull on the armature 121 is greatly increased because thepull-in gap now has a higher reluctance than the main gap 154. It may benoted, further, that as soon as the armature 121 of Fig. 13 moves, themain gap 154 is reduced and the pull-in gap is also reduced so that thereluctance of the main gap is decreased as is also the reluctance of thepull-in gap whereby a relatively strong pull upon the armature iseffected resulting in quick turning or pivotal movement thereof andmovement of the actuating rod 132 of Fig. 13.

It may be here pointed out that the relay will operate even though themagnetic reluctance of the magnetically reversible bar is not thermallychanged and this is effected by the ferromagnetic properties of theadjusting screw 131 of Fig. 13 and the magnetically reversible member128. Thus, if an excessive overload current should traverse the coil119, a very greatly increased ilux would be generated thereby and itwould traverse the magntic frame and the adjusting screw 131 andparticularly the point thereof, and the contact area of its engagementwith bar 127 would be highly saturated. The reluctance of the adjustingscrew and the magnetically reversible member would increase by magneticsaturation irrespective of any temperature change in the invar strip,which is analogous to an increase of resistance in portion 167 of Fig.23. As the area of the fiux path (air gap) between the armature 121 andthe portion 126 is relatively large and does not vary with the amount ofux traversing it, the pull-in torque will exceed the hold-out torque, sothat the armature will move upwardly substantially instantaneously andirrespective of any temperature rise of the magnetically-reversible bar.

I have found it very advantageous, in the operation of the device, toprovide the main gap hereinbefore described, as it tends to greatlyincrease the sensitivity of the device and make it operate more quicklyand definitely at certain current values without departing therefrom toany appreciable extent.

It may be noted that, since the armature bracket 56 is adjustable on thefront frame, the point of engagement between the gap-adjusting screw 77of Fig. 7 and the magnetically reversible bar 44 may be variedlongitudinally along the bar, and if the area of cross-section of thebar is uniform. the highest temperature will exist in the mid-portionand decrease towards each end thereof so that it is only necessary toadjust any given relay so that the armature is either centrally locatedthereof or to one side of the central line to obtain operation atdifferent current values. By using a magnetically reversible member ofthe type shown in Fig. 1,2 and designated by 111, a number of differentcurrent settings may be obtained and the temperature will be highestadjacent to one end portion and decrease toward the other end portion.This feature is disclosed and claimed in a copending application, SerialNo. 565,744, led Sept. 29, 1931 by C. H. Hodgkins and assigned to theWestinghouse Electric and Manufacturing Company.

As the member having a thermalig variable magnetic reluctance issupported substantially taneous reset characteristic.

out of engagement with the base and on an openturn coil, I have foundthat my improved relay has a very desirable characteristic, namely, thatit haswhat may be called a substantially instan- By this, I mean that ifthe relay has operated because of an excessive overload, it is possibleto reclose it substantially immediately and maintain it, or rather theswitch-arm 82, in closed position. This is because of the fact that, ifthe bar 44vis heated so that it becomes non-magnetic, it will be cooledvery quickly by reason of its being oonnected to and supported by theopen-turn energizing coil which is of such shape as to have not only arelatively low inherent ohmic resistance but also a relatively largeheat-radiating surface so that heat in the member 44 is conducted awaytherefrom very rapidly. The aprons 7l and [12, secured to the frontsurface of the base 31 and also to the magnetically reversible bar 44 atits ends are also effective in radiating heat generated in the bar 44.As was hereinbefore set forth, the relay is operated by electro-thermalaction alone, under one condition of operation, that is, when the coiland. the bar 44, or the heater 46, are traversed by a currentrepresenting a moderate overload. In this case, the member 44 graduallyheats, and loses its 'magnetic characteristic after a certain timedelay, causing the relay, or more particularly the armature, to beactuated as has already been hereinbeore set forth.

In case of a sudden excessiveoverload the relay will have aninstantaneous characteristic, that is, it will open without any timedelay, and this is accomplished because of the ferromagnetic saturationof a part of the hold-in magnetic circuit. It may here be pointed outthat, in addition to the increased reluctance of the lookout pin and ofthe magnetically-reversible bar caused by these parts being traversed byan increased main flux, the magnetically revers- Vible bar has itsmagnetic reluctance increased additionally as follows. When themagnetically reversible bar, which has a ferromagnetic characteristic istraversed by an excessive overload current, the current traversing themagnetic material will generate local flux lines Within the bar whichexist without dependence on the magnetization of the main magneticcircuit and are sufficient of Vthemselves to cause a high degree ofsaturation of the bar. On extreme overloads the internally producedsaturation in the bar is added to the effect of the externally producedsaturation (by the flux generated by the coil) in the bar and in thelockout pin to give a greatly increased reluctance of the lockout gap,while the reluctance of the pull-in gap is practically unchanged (itbeing mainly an air circuit). The pull-in torque thus increases muchmore rapidly than the lock-out torque and eiects instantaneous operationof the armature at high overloads irrespective of the temperature of themagnetically reversible bar. It may be noted that a local flux circuit(in the magnetically-reversible bar) and an external flux circuit (inthe core and magnetic frame and the bar) are present and areinter-linked.

It may be noted that, in the form of relay illustrated in Figs. l to '1,inclusive, the magnetically reversible current-conducting member 44 isnot only. supported by the ends of the coil sections but alsoelectrically connects them in series circuit relation, the location ofthe magnetically termined length of time, or it has `been lheated by anauxiliary heater. When this occurs the iiux traversing the armature 59and the lock-out pin 'i7 will continue to flow through the wider partsoffbar 44and into the apron '72, thus making it possible to obtainproper operation of the relay at different current values by adjustingthe armature (and particularly the lock-out pin 77) to engage the bar-44 yat different points along its length.

The con structure mustrated in Figs. a to 12,

inclusive, provides a relatively simple and highly efcient means forvarying the operating current of the relay, in that it is possible tolater- Aally slot the intermediate portion of the coil structure indifferent manners during the manufacture of the coil, so that a largernumber of current ratings are, therefore, obtainable. This coilstructure may be easily and quickly punched from a flat sheet of metaland then bent to shape substantially, as shown in the drawings.

The magnetic circuit structure hereinbefore described, and illustratedin the drawings, and various modifications coming within the scopethereof, permit a relatively delicate balance between the pull-in torqueand the hold-out torque, which balance is obtained by adjustment of theposition of the inner end of armature 59 by means of the adjustable nut'76. This means that, if the armature is properly adjusted for normalcurrent conditions in the relay, it will respond properly when anincreased currenttraverses the coil, thus providing a relativelysensitive relay. However, it is to be noted that the constructionaldetails hereinbefore set forth and including the use of a mainreluctance gap traversed by substantially all of the ux and otherdetails of the magnetizable frame structure assist greatly in increasingthe sensitivity of operation of my relay.

Various modications may be made in the device embodying my inventionwithout departing from the spirit and scope thereof and I desire,therefore, that only such limitations shall be placed on my invention asare imposed by the prior art or set forth in the appended claims.

I claim as my invention:

1. A thermal relay including a movable armature, amagnetically-reversible bar heated by the relay current, to control theposition ofthe armature, means including a pair of open-turn coilsections having one end of each section secured to the ends of themagnetically-reversible bar for assisting in dissipating the heattherein and supporting means for the coil sections and the bar securedto the other end of each coil section.

2. A thermal relay including a plural-section open-turn coil, endportions of each sec ion being located in spaced alinement, amagnetically reversible member electrically connecting the said alinedend portions of the coil sections, means for introducing and removingthe flux generated by said coil at spaced points in said magneticallyreversible member, the magnetomotive force generated by the currenttraversing said magnetically reversible member being additive to thatgenerated by the coil sections in said magnetically reversible member,and a movable armature controlled by said magnetically reversiblemember.

3. A thermal relay including an energizing coil, an armature magnetizedby, and movable relatively to, the coil, and a magnetically reversiblemember supported by, and electrically connected to, said coil inparallel-circuit relation therewith for controlling the position of thearmature.

4. A thermal relay including a movable magnetic armature, a magneticallyreversible member for controlling the position of the armature, and anenergizing coil having integral portions for directly supporting themagnetically reversible member and connecting it in shuntcircuitrelation to the coil, said coil embodying a portion of higher resistancebetween said supporting portions.

5. A relay including a movable armature and an energizing coil therefor,said coil having terminal portions and an intermediate portion which isalternately oppositely slotted to provide a current path of higher'electrical resistance than the terminal portions.

6. A relay including a movable armature and an energizing coil therefor,said coil having terminal portions and an intermediate portion which isalternately oppositely slotted to provide a circuitous path ofrelatively high resistance.

7. A thermal relay including a movable armasisting of shaped sheet metalbent to form al loop embodying terminal portions, lugs adjacent theterminal portions and an intermediate resistor portion, and meanssupported by the lugs for controlling the position of the armature.

8. A thermal relay including a movable armature, an energizing coiltherefor having terminal portions of relatively low electricalresistance, lugs adjacent to the terminal portions and a resistorportion of relatively high electrical resistance between the terminalportions, and a magnetically reversible member electrically connectedto, and supported by, the lugs and controlling the position of thearmature.

9. A thermal relay including.-I an energizing coil comprising a sourceof magnetomotive force, a movable armature, and a frame structurecooperating With the movable armature to provide a magnetic circuit forthe flux and including a main reluctance portion magnetized by saidcoil, and two parallel-related reluctance portions in series magneticcircuit with the main reluctance portion, one of the twoparallel-related portions including a magnetically reversible membercontrolling the position of the armature by the variation of itsmagnetic permeability.

l0. In a thermal relay having an energizing coil, a flux-carryingstructure magnetized by said coil and including xed and movable membersproviding parallel-related magnetic circuit potions, and a main magneticcircuit portion in series relation to the parallel-related portions, oneof the parallel-related magnetic-circuit portions having athermally-variable magnetic characteristic and controlling the positionof the movable member, a part of the main magdetermined temperaturegradient in the thermally variable member.

12. In a thermal relay including a movable armature, a magnetic circuitstructure for controlling the position of the movable armature andincluding a main gap and a pull-in gap in series relation, a hold-outmagnetic circuit portion shunting the pull-in gap and having normally arelatively low magnetic reluctance to substantially short circuit thepull-in gap and hold the armature in a predetermined position.

13. In a thermal relay having an energizing coil traversed by a varyingcurrent, and a movable armature, a magnetic circuit structure forcontrolling the position of the movable armature and including a maingap and a pull-in gap in series relation and a hold-out magnetic circuitportion shunting the pull-in gap and hav- ,A ing a relatively lowmagnetic reluctance at less than a predetermined current value in thecoil to substantially short circuit the pull-in gap and normally holdthe armature in a predetermined position.

14. In a thermal relay having an energizing coil traversed by a varyingcurrent, and a movable armature, a magnetic circuit structure forcontrolling the position of the movable armature and including a maingap and a pull-in gap in series relation and a hold-out magnetic circuitportion shunting the pull-in gap and including a member in electriccircuit with the coil and having a thermally variable magneticcharacteristic normally having a relatively low magnetic reluctance tosubstantially short circuit the pull-in gap and hold the armature in apredetermined position at less than a predetermined current value.

15. In a thermal relay having an energizing coil traversed by a varyingcurrent, and a movable armature, a magnetic circuit structure forcontrolling the position of the movable armature and including a maingap and a pull-in gap in series relation and a hold-out magnetic circuitportion shunting the pull-in gap and including a member in electriccircuit with the coil and having a thermally variable magneticcharacteristic normally having a relatively low magnetic reluctance tosubstantially short circuit the pull-in gap and hold the armature in apredetermined position at less than a predetermined current value,'thereluctance of the member having the thermally variable magneticcharacteristic increasing greatly at current values in the coil abovesaid predetermined value to thereby cause energization of the pull-ingap and effect movement of the armature.

16. In a thermal relay having `a variable-current-traversed coil and amovable armature, 'a magnetic circuit' structure for the flux generatedby thc coil including a main gap having a predetermined reluctance and apull-in gap having a greater reluctance than the main gap in seriesrelation therewith, and a hold-out magnetic portion short circuiting thepull-in gap and having normally a vrelatively low magnetic reluctance-which increases with increase of temperature of the portion whereby theshort circuit across the pull-in gap is substantially removed at apredetermined temperature of said lhold-out portion thereby energizingthe pull-in gap and effecting movement of the armature.

1'1. In a thermal relay having an energizing coil, a movable armatureenergized by the coil, and a frame structure cooperating with thearmature to provide a flux path traversed by the main ux produced bysaid coil, and two parallel-related flux paths in series circuit withthe path traversed by the main flux, one of said parallel-related fluxpaths comprising means for effecting movement of the armature with atime delay on moderate overloads in the coil and for effectinginstantaneous movement of the armature on excessive overloads in thecoil.

18. VIn a thermal relay having an energizing coil, a movable armatureenergized by the coil, and a frame structure cooperating with thearmature to provide a flux path traversed by the main flux produced bysaid coil, and two parallel-related ilux paths in series circuit withthe path traversed by the main ux, one of said parallel-related fluxpaths comprising means for eiecting movement of the armature byelectro-thermal action of said means when 'the coil is traversed by acurrent representing a moderate overload and by electro-magnetic actionof said means when the coil is traversed by a current representing anexcessive overload.

19. In a thermal relay having an energizing coil, a movable armatureenergized by the coil, means for normally biasing said armature to openposition, and a frame structure cooperating with the armature to providea flux path traversed by the main flux produced by said coil, and twoparallel-related flux paths in series circuit with the path traversed bythe main ilux?, one of said parallel-related flux paths comprising meansfor normally magnetically short-circuiting the other parallel-relatedpath to hold the armature in its initial position and for removing saidshort circuit to. effect movement of the amature on overload currents inthe coil, said other parallel-related path operating to produce a,pull-in force on the movable armature.

20. In a thermal relay having an energizing coil, a movable armatureenergized by the coil, means for normally biasing said armature to openposition, and a trame structure cooperating with the armature to providea high reluctance ilux path traversed by the main iiux produced by saidcoil, and two parallel-related ilux paths in series circuit with thepath traversed by the main flux, one of said parallelrelated flux pathscomprising means for normally magnetically short circuiting the otherparallel-related path to hold the armature in its initial position andfor' removing said short circuit with a time delay on moderate overloadsin the coil and instantaneously on excessive overloads in the' coil toeiectmovement of the armature, said other parallel-related pathoperating to produce a pull-in force on the movable' amature and alsohaving a high reluctance.

21. In a thermal relay having a movable armature and a member having athermally variable magnetic characteristicv for controlling the positionof the armature and effective to cause movement of the armature upon apredetermined temperature rise of the member, and

means for eecting a substantially instantaneous reset of the switchincluding a pair of open-turn energizing coils directly connected to andsupporting the member to assist in dissipating heat therefrom.

22. In a thermal relay having a movable armature and a member having athermally variable magnetic characteristic for controlling the positionof the armature and eiective to cause movement of the armature upon apredetermined temperature rise of the member, and means for effecting asubstantially instantaneous cooling of said armature-controlling memberincluding an energizing coil directly connected to, and supporting, saidarmaturecontrolling member.

23. In a thermal relay having a movable armature and a member having athermally variable magnetic characteristic for controlling the positionof the armature and effective to causemovement of the armature upon apredetermined temperature rise of the member,

means for eiecting a substantially instanta' neous cooling of saidarmature-controlling member including an energizing coil directlyconnected to, and supporting, said armaturecontrolling member, andadditional supporting means for the armature-controlling member, saidadditional supporting means having a relatively large area of heatradiating surface.

24. A thermal relay including a source of magnetomotive force, a movablearmature energized thereby and means for controlling the position of thearmature, including a heated magnetically reversible bar having atemperature gradient in only one direction thereof and means including amagnetic member adjacent to the low temperature end of the bar fordirecting the flux in the magnetically reversible bar to thelow-temperature part thereof.

25. A thermal relay including an energizing coil comprising a source ofmagnetomotive force, a flux-carrying structure having a fixed portionand a movable portion carrying substantially all of the ux produced bysaid coil, and two parallel-related flux-carrying portions in seriescircuit with iixed and movable portions, one of said parallel-relatedportions including an air gap of relatively large area of cross sectionand the second parallel-related portion including a variable-reluctanceelement.

26. A thermal relay comprising a magnet having a pull-in pole-piece anda hold-out polepiece, a current-heated, thermally responsive,magnetically variable, magnetizable element 1ongitudinally disposed inmagnetic series relation to the flux in said hold-out pole-piece, saidelement being of a material which loses its magnetic quality at apredetermined temperature, and a movable armature associated with saidmagnet and subject to the opposing attractions of said pole-pieces,being normally attracted by said hold-out pole-piece.

2'7. The invention as defined in claim 26, characterized by said pull-inand hold-out polepieces being of the same polarity, whereby the magneticiiux-paths thereof are in parallel-circuit relation.

28. A thermal relay comprising a currentenergized electromagnet having apull-in polepiece, a movable armature associated with said magnet andsubject to the attraction `oi said pull-in pole-piece, and means fornormally holding the armature away from said pull-in polepiece so as tobe separated therefrom by an airgap, characterized by a magnetic pathshunting said air-gap and comprising a current-heated, thermallyresponsive, magnetically variable, magnetizable element whichsubstantially loses its magnetizable quality at a predeterminedtemperature, said magnetic shunting path also including a portion whichbecomes substantially saturated on extremely large flux densitiescorresponding to extremely large overcurrents.

29. A thermal relay comprising a currentenergized electromagnet having apull-in polepiece and a hold-out pole-piece, a currentheated, thermallyresponsive, magnetically variable, magnetizable element being inmagnetic series relation to the flux in said hold-out polepiece, saidelement being of a material which loses its magnetic quality at apredetermined temperature, a magnetic-path-section being alsoin magneticseries circuit relation to the flux in said hold-out pole-piece andhaving the property of becoming first substantially saturated onextremely large ux densities corresponding to extremely largeovercurrents, and a movable armature associated with said magnet andsubject to the opposing attractions-of said polepieces, being normallyattracted by said hold-v out pole-piece.

30. The invention as defined in claim 29, characterized by said pull-inand hold-out polepiecesbeing of the same polarity, whereby the magneticflux-paths thereof are in parallelcircuit relation.

31. A relay comprising a magnet having a pull-in pole-piece and ahold-out pole-piece, and a movable armature associated with said magnetand subject to the opposing attractions of said pole-pieces, beingnormally attracted by said hold-out pole-piece, characterized by asaturable magnetizable member in magnetic seriesv relation to the fluxin said hold-out pole-piece, and means responsive to the relay currentfor bringing about a saturated condition in said magnetizable member onexcessive overloads.

A 32. The invention as dened in claim 31, characterized Ly said pull-inand hold-out pole-pieces being of the same polarity, whereby themagnetic flux-paths thereof are in parallel-circuit relation.

33. A relay comprising a magnet having a pull-in pole-piece and ahold-out pole-piece, and a movable armature associated with said magnetand subject to the opposing attractions of said pole-pieces, beingnormally attracted by said hold-out pole-piece, characterizedby asaturable magnetizable member in magnetic series relation to the flux insaid hold-out pole-piece, and means for causing a current to traversesaid magnetizable member, in response to said relay current, forbringing about a saturated condition in said magnetizable member onexcessive overloads.

34. The invention as defined in claim 33, characterized by said pull-inand hold-out polepieces being of the same polarity, whereby the magneticflux-paths thereof are in parallel-circuit relation.

35. A relay comprising a current-responsive electromagnet having apull-in pole-piece and a hold-out pole-piece, and a movable armatureassociated with said magnet and subject to the opposing attractions. ofsaid pole-pieces, being normally attracted bysaid hold-out pole-piece,characterized by a saturable magnetizable member in magnetic seriesrelation to the flux in said hold-out pole-piece, said magnetizablemember being included in the coil of said electromagnet, whereby thecurrent traversing the same assists in effecting a saturated conditiontherein on excessive overloads.

y36. The invention as defined .in claim 35, characterized by saidpull-in and hold-out polepieces being of the same polarity, whereby themagnetic flux-paths thereof are in parallel-circuit relation.

37. In a thermal relay having an energizing coil, a movable armatureenergized by the coil, means for normally biasing said armature to openposition, and a frame structure cooperating with the armature to providea high-reluctance flux path traversed by the main flux produced by saidcoil, and two parallel-related flux paths in series circuit with thepath traversed by the main flux, one of said parallelrelated flux pathscomprising means for normally magnetically short-circuiting the otherparallel-related path to hold the armature in its initial position andfor removing said short circuit to effect movement of the armature onoverload currents in the coil, said other parallelrelated path operatingto produce a pull-in force on the movable armature and also having ahigh reluctance.

38. A relay comprising a source of magnetomotve force, a magnetic fluxstructure energized thereby and including a field member and a movablearmature normally separated from the field member by a pull-in gap ofrelatively high reluctance,and means for normally biasing said armatureto open position, characterized by said magnetic flux structurecomprising a main flux path of relatively high reluctance, and twoparallel-related flux paths in series with said main ux path, one ofsaid parallelrelated flux paths including said pull-in gap of relativelyhigh reluctance, and the other of said parallel-related flux pathscomprising a variable-reluctance means which is normally of relativelylow reluctance, so as to magnetically short-circuit saidparallel-related pull-in flux path, and means for, at times, changingsaid variable-reluctance means so as to cause it to have a relativelyhigh reluctance.

39. A relay comprising a source of magnetomotive force, a magnetic fluxstructure energized thereby and including a field member and a movablearmature normally separated from the field member by a pull-in gap ofrelatively high reluctance', and means for normally biasing saidarmature to open position, characterized by said magnetic flux structurecomprising a main flux path of relatively high reluctance, and twoparallel-related flux paths in series with said main flux path, one ofsaid parallelrelated flux paths including said pull-in gap of relativelyhigh reluctance higher than said main flux path, and the other of saidparallel-related fiux paths comprising a variable-reluctance means whichis normally of relatively lw reluctance, so as to magneticallyshort-circuit said parallel-related pull-in flux path, and means for, attimes, changing said variable-reluctance means so as to cause it to havea relatively high reluctance higher than said parallel-related pullinflux path.

40. A relay comprising a current-responsive energizing coil, a magneticflux structure energized thereby and including a field member and amovable armature normally separated from the field member by a pull-ingap of relatively high reluctance, and means for normally biasing saidtion. characterized by said magnetic ilux strucarmature to openposition, characterized by said magnetic ilux structure comprising amain ilux path of relatively high reluctance and two parallel-relatedilux paths in series with said main ilux path, one of saidparallel-relatedilux paths including said pull-in gap of relatively highrey luctance, and the other ot said parallel-related flux pathscomprising a variable-reluctance means which is normally of relativelylow-reluctance, so as to magnetically short-circuit saidparallel-related pull-in ilux path, and means for, at times, changingsaid variable-reluctance means so as to cause it to have a relativelyhigh reluctance.

4l. A relay comprising a current-responsive energizing coil, a magneticilux structure energized thereby and including a ileld member and amovable armature normally separated from the eld member by a pull-in gapof relatively high reluctance, and means for normally biasing saidarmature to open position, characterized by said magnetic flux structurecomprising a main ux path oi relatively high reluctance, andtwo'parallel-related flux paths in series with said main iiux path, oneof said parallel-related flux paths including said pull-in gap pflrelatively high reluctance higher than said main ilux path, and theother of said parallel-related flux paths comprising avariable-reluctance means which is normally o! relatively lowreluctance, so as to magnetically short-circuit said parallel-relatedpull-in tlux path, and means for, at times, changing saidvariable-reluctance means so as to cause it to have a relatively highreluctance higher than said parallel-related pull-in flux path.

42. A relay comprising a current-responsive energizing coil, a magneticilux structure energized thereby and including a ileld member and amovable armature normally separated from the ileld member by a pull-ingap, and means for normally biasing said armature to open positurecomprising a main ilux path and two parallel-related ilux paths inseries with said main ilux path. one of said parallel-related ilux pathsincluding -said pull-in gap, and the other o! said parallel-related fluxpaths comprising a variable-reluctance means which is normally o!relatively low reluctance, so as to magnetically short-circuit saidparallel-related pull-in ux path, said variable vreluctance meanscomprising a thermally responsive magnetically reversible element and asaturable element in series, and current-responsive means for heatingsaid magnetically reversible element, whereby, on moderate overloads,the thermally responsive element will remove the short-circuit on thepull-in ilux path so as to effect movement of the armature after a timedelay, whereas, on excessive overloads, the saturable element willremove the short-circuit on the pull-in flux path so as to effectsubstantially instantaneous movement o! the armature.

43. A relay comprising a current-responsive energizing coil, a magneticilux structure energized thereby and including a eld member and amovable'armature normally separated from the ileld member by a pull-ingap, and means for normally biasing said armature to open position,characterized by said magnetic ux structure comprising a main ilux pathand two parallelrelated flux paths in series with said main iiux path,one of said parallel-related ilux paths including said pull-in gap, andthe other of said parallel-related ilux paths comprising a variablereluctance means which is normally o! relatively low reluctance, so asto magnetically short-circuit said parallel-related pull-in ilux path,said variable reluctance means comprising a saturable and thermallyresponsive magnetically reversible element in electrical circuitrelation to said coil.

WILLIAM J. HUDSON.

